Cupric estimation

In REACT, we prepare the calculation by disenabling the redox couple between trivalent and pentavalent arsenic (arsenite and arsenate, respectively). As well, we disenable the couples for ferric iron and cupric copper, since we will not consider either ferrous or cupric species. We load dataset FeOH+.dat , which contains the reactions from the Dzombak and Morel (1990) surface complexation model, including those for which binding constants have only been estimated. The procedure is... 

Iodometry is an indirect procedure based on the aforesaid reversible reaction whereby the assay of oxidizing agents, for instance available chlorine in bleaching powder, cupric and ferric salts may be carried out by reducing them with an excess potassium iodide thereby liberating an equivalent quantity of iodine which can be estimated using a standard solution of thiosulphate. 

This double salt is made easily by dissolving potassium chloride, KC1, and cupric chloride, CuCl2-2H20, in water in the proportion of two molecules of the former to one of the latter and evaporating the solution to crystallization. This salt, as well as the corresponding ammonium salt, is used in the determination of carbon in iron. Iron dissolves in a concentrated solution of the salt, leaving the carbon undissolved, and the latter can be filtered off and estimated by combustion. 

Estimates of the effective encounter distance, f eff, and diffusion coefficient, D, from quenching of triplet phenanthrene by cupric ions in methanol—water mixtures (Butler and Pilling [200])... 

Vanadium predpitates the metal from solutions of salts of gold, silver, platinum, and iridium, and reduces solutions of mercuric chloride, cupric chloride and ferric chloride to mercurous chloride, cuprous chloride, and ferrous chloride, respectively. In these reactions the vanadium passes into solution as the tetravalent ion. No precipitation or reduction ensues, however, when vanadium is added to solutions of divalent salts of zinc, cadmium, nickel, and lead. From these reactions it has been estimated that the electrolytic potential of the change, vanadium (metal)—>-tetravalent ions, is about —0 3 to —0 4 volt, which is approximately equal to the electrolytic solution pressure of copper. This figure is a little uncertain through the difficulty of securing pure vanadium.5... 

We first used the model described to estimate the equilibrium potential for the electron transfer reaction. We took considerable trouble, some of which is described here with more detail in Ref. 69, to assure that the equilibrium potential was reasonably well-described by the model, because if a simulation model does not correctly reproduce the electrode charge density at which the two ionic charge states are in equilibrium, then the simulation may proceed in a very unrealistic electrostatic environment. This can lead to qualitatively misleading results. Unlike the ferrous-ferric reaction, the cuprous-cupric... 

Our calculations of the activation free energy barrier for the cuprous-cupric electron transfer were not precise enough to permit a very accurate estimate of the absolute value of the exchange current for comparison with experiment. In principle, a determination of the absolute rate from the activation energy requires a calculation of the relevant correlation function [82] when the ion is in the transition region within the molecular dynamics model. We have not carried out such a calculation, but can obtain some information about the amplitude by comparing experiments with the transition state theory expression [84]... 

The oxidation of methane was very slow under the experimental conditions employed The slowest rates are those with anhydrite as oxidant. Because the ratio of the rate constants, a, is dependent upon the oxidant, it is difficult to estimate the carbon isotope selectivity during sulfate reduction at temperatures relevant to TSR in sour gas occurrences. However, the effects are substantial with the cupric oxide-manganese dioxide and hematite-anhydrite trends in Figure 2 giving extrapolated a-values of about 1.02 and 1.04 respectively at 200°C. 

In a consideration of the reduction of cupric acetate, if the solubility of hydrogen is taken to be independent of temperature (known to be nearly so in the range considered), then for an a estimated to be 6.4 X 10-4 moles atm.-11.-1... 

These simulation programs, based on a perturbation approach, have been used to estimate the metal-metal distance for a number of dipolar-coupled ( 2 J < 30 cm-1) cupric complexes (Boyd, P. D. W. et al. J. Chem. Soc. Dalton, 1549 (1973)) and show good agreement when compared with x-ray crystallographic results... 

There is a great variety of quantitative methods available for the estimation of copper. Gravimetrically it is estimated as cupric oxide, obtained by ignition of the precipitated hydroxide by precipitation as sulphide, and ignition in an atmosphere of hydrogen to cuprous sulphide by precipitation as cuprous thiocyanate, CuCNS, this salt being either weighed directly, or converted into cuprous sulphide and by electrolytic... 

A gasometric method for the estimation of cupric salts is based on the reduction of cupric-ammonia solutions by a hydrazine salt, a cuprous-ammonia solution being formed, and the hydrazine oxidized to nitrogen and water ... 

Some other colorimetric assays involving diazotization with p-nitroaniline and nitrous acid (34), use of folin and Cioalteu phenol reagent (35), complexation with cupric ion in nitrous acid (36-38) or estimation as the nitro derivative (39) have been reported in the literature. 

Adequate computer simulation usually requires accurate values for g, and gjs, together with good estimates for g, A and Replication of the experimental spectrum should require only small changes in the input parameters. A table of g and A values for several cupric complexes is useful for comparison with the experimentally determined parameters [192]. If A is larger than 120 G, then the compound is square planar or distorted square planar if A is less than 120 G the complex shows distortion toward a tetrahedral configuration [192], The latter type of complex is usually characterized by a strong blue color. 

The ESR spectrum for cupric ion bound to four equivalent imidazoles from carnosine ()8-alanyl-L-histidine dipeptide) in frozen solution shows the quality of information that can typically be obtained [233] (Fig. 15, top spectrum). The intense line on the right split by at least nine hyperfine lines is the gj feature resolved due to hyperfine splitting to copper and to nitrogen donor atoms. Three of the four copper hyperfine lines in the gy (2.25) region (left side) are observable with y4 [ = 175 G. The remaining ESR parameters can be estimated and confirmed by computer simulation. These values for carnosine aregy = 2.06, Af = 15 G and /4 = 15 G. For comparison, data for cupric ion bound to hemoglobin at the N-terminus are gy = 2.210, = 2.050,... 

Biphenyl coupling occurs to some extent on cupric oxide oxidation of lignin model compounds [55,56]. This indicates that the value derived from permanganate oxidation studies is slightly too high. On the basis C NMR examinations, Drumond et al. [57] arrived at a higher value for the frequency of biphenyl units (24-26%). The accuracy of this estimate can be questioned, since no separate signals from biphenyl units can be discerned in the spectra. 

---